Steam system for continuous cleaning of hood fans

ABSTRACT

A device and method for cleaning fans in range or stove hoods by spraying steam onto the fan impeller area on which soot and cooking fumes condense to clean the impeller and wash the accumulated condensates down a drain. By using steam above atmospheric pressure as the cleaning fluid, the device uses significantly less water that other devices that spray water or an aqueous solution to clean the fan blades.

RELATED APPLICATIONS

This application is based on U.S. patent application Ser. No. 11/600,469, filed 16 Nov. 2006, which application is based on provisional application 60/772,182, filed Feb. 10, 2006, the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a system for continuously cleaning fans operating in a ventilation hood for a stove or other cooking device.

Kitchen vent or exhaust systems are commonly used to remove steam, odors, and other airborne vapors resulting from cooking on stoves. The exhaust systems often include grease filters to capture grease carried by the airborne vapors. For homes and smaller establishments, the most common is an up draft system utilizing a hood covering a portion or all of the stove burners to capture the rising air. The hood is attached to the wall, or in the case of a kitchen island, is suspended from the ceiling. Conventional vent hoods typically are cone shaped and include a centrally positioned fan which provides a centralized suction to draw air into the hood. Stove hoods are well-known in the cooking appliance arts for exhausting steam and smoke from the cooking area. Such devices generally include a hood and at least one fan in the hood area blowing from the hood to an exhaust duct. Over time, smoke particles, aerosols, and volatiles from the cooked food adhere and/or condense onto the surfaces of the hood, including the fan blades. The fans used are typically axial fans, although radial fans can also be used.

There are various disclosures of systems for cleaning the fan blades of hoods over stoves. Some systems utilize a reservoir adjacent the fan, where the fan motor causes reservoir fluid to be sprayed onto the fan blades; the liquid can be recycled to the reservoir, and replaced when desired. Other systems rely on tap water or hot water, optionally including a detergent or surfactant, sprayed onto the fan blades, and then collected and discharged, or retained for later removal. Still other systems ignore the fan blades but have a pipe running into the exhaust conduit or duct, and the pipe including nozzles for spraying against the inner conduit surface to remove cooking residue therefrom. Some systems combine cleaning of the duct and the fan blades. These systems are analogous to systems for cleaning turbine blades. Other systems treat the exhaust gas stream with a spray prior to its entry to the hood to wash the volatiles and smoke particles from the exhaust gas so that less has to be cleaned from the hood, fan, and exhaust conduit surfaces. Various systems include a filter disposed downstream or upstream of the exhaust fan for removing smoke and aerosols, and further include a spray that occasionally or continuously washes the filter.

These systems are described in the following U.S. patents and published applications, the disclosures of which are incorporated herein by reference: U.S. Pat. Nos. 3,616,744; 3,805,685; 3,854,388; 4,085,735; 5,158,429; 5,860,412; 6,047,694; 6,503,334; 6,662,800; 6,712,068; 6,732,729; 6,880,551.

For devices that fit under a hood, or within a hood enclosure, a source of water can be roughed in to the wall behind the stove area. Accordingly, all that is needed for such devices is a valve, which may be essentially controlled by a pump (e.g., the cost of an electronic control valve using the existing water system pressure can be more expensive than a small electric pump connected to a valve at the fan housing). For those devices that provide heated water, electricity is taken from the local source used for the fan to power a heating coil immersed in a reservoir for the water. The prior art devices show a fluid being provided to the fan housing by a pump, so the fluid must be liquid.

SUMMARY OF THE INVENTION

In light of the foregoing, an object of this invention is to provide a better cleaning system for hood fans. In particular, by using steam, the condensed aerosols and volatiles and smoke particles are more easily removed from the fan blades. Also, by using steam there is no need to add a detergent or surfactant to an existing source of water.

In general, this invention provides an exhaust hood with at least one fan and a pressurized steam source supplying steam to impinge on the fan blades. That is, this invention provides device and method for cleaning fans in range or stove hoods by spraying steam onto the fan impeller area on which soot and cooking fumes condense to clean the impeller and wash the accumulated condensates down a drain. By using steam as the cleaning fluid, the device uses significantly less water that other devices that spray an aqueous solution.

One embodiment of the invention comprises an exhaust hood defining an enclosure and having an orifice adapted for attachment to exhaust duct, a fan disposed in the enclosure and having an output in fluid communication with the orifice, a steam generating for producing steam above atmospheric pressure from a water supply, and a conduit for channeling the high pressure steam to blades of the fan. In preferred embodiments, there is a gutter to collect condensed steam from the fan blades, the flow of water into the steam generator is controlled by a pump, the steam generator has emergency safeties, and/or the conduit has a nozzle.

In another embodiment, this invention provides a method for degreasing the impeller of a fan mounted in a cooking exhaust hood, comprising providing a hood installation including said fan, heating water to steam in a vessel pressurized above atmospheric pressure, and directing pressurized steam from said vessel against the impeller of said fan in an amount effective to degrease the impeller.

Viewed another way, this invention provides a device for cleaning the impeller of a fan installed in a hood ventilating a cooking area, said device directing a fluid onto the impeller and draining water from the impeller, the improvement comprising a steam generator for generating steam as said fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exploded view of the steam generator and pump.

FIG. 2 depicts a range hood installation including a cut-away perspective showing two fans, a steam generator, and a user-accessible controller on the outer surface.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The invention is for a device and method for continuously cleaning, or degreasing, fan impellers in hoods used for exhausting stovetops or cooktops (the former being used in an exemplary manner herein). The hood is typically mounted on a wall against which the stovetop is installed, or suspended over a stovetop installed on an island. The hood can be a simple canopy, or it can include a housing in which the fans are supported. Water is fed to a steam generator, preferably disposed within the housing of a hood. Steam is generated at a pressure above atmospheric pressure, and the pressurized steam is directed by a conduit to the fan impeller, preferably so that the hub, the blades, and any other part of the impeller that normally comes into contact with the cooking fumes being exhausted is impinged by the steam. Because there is no superheater for the steam generated, the pressurized steam is essentially saturated steam at elevated pressure and temperature.

As shown in FIG. 1, the steam generator 101 preferably comprises an outer housing 103 having a base 105 and a cover 107. Disposed within the outer housing is the inner steam generating housing 109, comprising a generator base 111 (preferably about 1300 W) and a generator cover 113. When the base and cover are attached, a steam generating volume is defined. Heat can be provided to the generator by any means, including gas burners, but preferably the base includes an resistive/inductive heating coil 115. The generator base and cover are joined by a high pressure (and temperature) seal 117 at the periphery where they mate. Disposed within the steam generating volume can be a plate 119. The plate can have a high surface area (e.g., with hills or upstanding flanges as shown, and optionally openings), the bulk which adds to the thermal inertia of the steam generating volume and the hills and holes providing increased surface area for generating steam when the plate is at temperature. The plate can be attached to the base or it can be dimensioned to fit immovably between the base and cover, in which case preferably a spring 116 is disposed between the plate and the cover. The plate can be provided with small holes to act like a separator, whereby inlet water is maintained near the base and heated to steam that escapes through the holes into the cover region on the other side of the plate.

Water is supplied preferably to the center 121 of the steam generator base. In a preferred embodiment, water from lines roughed into the wall behind the stovetop is supplied to a pump 123 (shown with electrical contacts on the top for connecting to a power supply and control); the pump is designed, like a check valve, to prevent water from moving from the steam generator back through the pump. The pump increases the water pressure and forces the water through a tube 125 connected to the steam generator base center. The pump is preferably mounted to the base of the housing as part of a sold unit, but can be mounted elsewhere, preferably on the unit.

At the top of the steam generator is an orifice 127 disposed accessible or within an opening 129 in the cover. A conduit 301 connects the orifice to a second orifice 305 a/b in a housing 307 surrounding the exhaust fan 309 disposed in the range hood. As shown in FIG. 2, a cut-away perspective of a hood installation, the fan is centered in a housing disposed around the periphery of the fan. The fan housing includes at least one if not two or more orifices where steam can be introduced. As shown in the drawing, one orifice directs the steam supplied from the steam generator radially inwardly against the blades and hub. Alternatively, one or more orifices can be provided on just the top portion (e.g., at or above the blades) or just the bottom portion (e.g., below or at the blades). As shown, the housing can include a pair of gutters 311 a/b or a single gutter (that is, without the center wall) to collect steam condensate and degreased debris flung centrifugally by the fan onto the inner portion of the housing. A single gutter is preferred because there is less surface area on which debris can accumulate. The collected condensate is removed by the drainage tubes 313 to a waste water pipe also roughed in to the wall, or to a container for collection at a later time. The second orifice is shown penetrating the gutters (and thus is actually a plurality of orifices) to direct the steam supplied by the steam generator axially in the direction of the incoming cooking fumes.

The steam generator is designed to generate steam at a pressure above atmospheric, preferably significantly above atmospheric. Thus, the steam generator is pressurized. The water supply pump must be able to supply water at the designed operating pressure, overcoming the pressure in the steam generator. Disposed in the outlet in the steam generator cover, and/or attached to the orifice(s) in the fan housing, most preferably on the inside wall of the housing proximate to the fan blades and hub, is a nozzle 315 creating a backpressure and creating a spray of steam directed at the fan blades and housing where there cooking fumes first contact the fan. Alternatively, the conduit connecting the steam generator cover to the orifices in the fan housing can be sized to provide the backpressure needed for the desired operating pressure without a separate valve.

The steam generator parts are preferably made of aluminum, stainless steel, or any other suitable material, preferably metal. The steam outer housing cover is preferably plastic or metal, and the outer housing base is preferably metal. The water tube from the pump to the steam generator base can be plastic or metal.

The steam generator and pump are preferably controlled by simple means to provide the pressurized steam as well as safe operation. A temperature regulator 141 senses the temperature of the steam generator base and/or the temperature within the steam generating volume. Such devices (and all of the other parts required for this invention) are commercially available or can be easily manufactured. Preferably there are two temperature regulators, 141 and 143. A single temperature regulator is preferably set (and fixed at the factory) to a temperature of between about 175° C. and about 200° C. At that temperature, saturated steam has a pressure of about 225 psia, or about 15.5 times atmospheric pressure; it can be considered as pressurized steam with respect to that generated at ambient pressure. A temperature, voltage, and/or current activated fuse 145 is used to provide a safety if there is insufficient water on the heating surface; preferably a temperature based fuse to shut off at about 220° C. (about 340 psia), more preferably about 216° C., is used. In the embodiment shown with two temperature regulators, preferably one is set to about 130° C. (equivalent to about 35 psia) and the other is set to about 175°-200° C. It is preferable to have a temperature of at least about 120° C., and more preferably at least about 140° C., and most preferably at least about 175° C. to generate sufficient pressure for an adequate supply of steam. A pressure relief valve is preferably included in the cover. The temperature regulator can toggle the resistance heater on and off to maintain the desired temperature in the steam generating volume. When two temperature regulators are used, the system will heat until the higher set point temperature is reached, and then the heater is turned off; if there is time remaining in the cleaning cycle, if the temperature falls below the lower set point temperature (i.e., 130°), the resistance heater will start heating again to maintain steam generation. In operation, the device cycles between from about 140° C. (52 psi for saturated steam) up to about 215° C. (311 psi for saturated steam), shuts off the heater, and then restarts when the low set point is reached. The spring (which instead can be one or more leaf springs, although a helical spring is shown) prevents the plate from contacting and blocking the orifice, and also prevents chattering of the plate within the generator. The spring also acts to force the plate in contact with the generator so that it heats and can be used as a thermal mass to heat the water.

Supply water can be held in a small reservoir 280 from which the pump feeds, and a low reservoir level sensor (not shown) can be used to shut off the pump and/or the heating coil if the reservoir level is too low. As mentioned, the reservoir can be fed by plumbing roughed-in behind the stove and hood, or the reservoir can be attached to a wall or the top of the hood with a door accessible by the user for manually filling the reservoir. A preferred reservoir size is about 1.6 L (about 0.4 gallons), and a low shut-off sensor is preferably provided set to about 0.3 L. The reservoir preferably includes a water level sensor (preferably electrical) that will shut off the system, or prevent the system from being started, if sufficient water is not present in the reservoir.

As pressure builds in the steam generating volume, steam exits the outlet and impinges on the fan after passing through at least one nozzle. While not desirous of being constrained to a particular theory, it is believed that the significantly enhanced enthalpy of the fluid impinging the fan acts to degrease the fan without the need for the addition of a detergent or surfactant to the water supply. For example, even with expansion of the steam through a valve, the steam has an enthalpy significantly higher than hot water, and about four times boiling water at atmospheric pressure. Accordingly, the operator is not burdened with having to buy detergent and refill the reservoir of the prior art devices on a regular basis, else the degreasing efficiency is decreased. In areas of hard water, it may be desirable for the present device to have a small reservoir feeding the pump to allow for the addition of vinegar or another additive to clean scale from inside the steam generator. Although geometry of the volume defined by the steam generator, tubing, and nozzle, in combination with the vapor flow rate, heat input, water pump pressure, and pressure drops may likely affect whether the spray includes some water droplets (i.e., a mixed vapor-liquid phase is produced), the intent is to impinge as much steam (vapor phase) as possible on the impeller because there is significantly more energy available for degreasing in steam than in water, and because a lower ratio of liquid to vapor generated (at the nozzle outlet) means less water will be used. It is critical that pressurized steam, saturated steam above ambient pressure (optionally superheated), be produced from the steam generator so that effluent from the generator exits the nozzle stays and impinges the impeller blades as steam and not a finely divided liquid spray.

Of course, the size and length of the conduit (including any cooling therein), and any decrease in the amount or heat value of steam after expansion through the valve, will have an effect the efficiency if not compensated in the design. What is important is the generation of steam above atmospheric pressure at a pressure and rate sufficient to provide an adequate flow of steam against the fan impeller. Unlike a commercial installation where there is significant ductwork upstream of the exhaust fan, and the exhaust fan is located at the duct exit, at the building exterior, a home kitchen typically has a cooking ventilation system with the exhaust fan at the duct intake. Home cooking ventilation ducts are rarely cleaned because there is a relatively short distance between the fan and the exterior exhaust, and the fan can exhaust the air by pushing it out before vapors condense and particles settle. A commercial installation ventilates higher and smokier volumes, through longer distances, and so the fan is positioned at the exit. In a home hood installation, the fan (and any filter that might be positioned in front of the fan) is a prime location for the accumulation of grease and vapor condensation because the that surface is the first contacted by the cooking vapors and smoke. Thus, while there are systems for cleaning the exhaust stream and associated ducts in commercial settings, the present invention is especially adapted for cleaning the fan in a home ventilation installation. The figures presented herein are drawn to scale to the extent that the pressurized steam generator has a low profile, or a high aspect ratio, enabling it to be placed within the enclosure of the hood installation in a typical home setting, thus utilizing available space within the enclosure. As shown, the parts of the steam generator are plate-like or pan-like, creating a low profile (span to height ratio) that does not require significant space for placement entirely within the hood enclosure, and with relatively simple connections to readily available power and water supplies adjacent the stove area of a typical home kitchen (or just electricity if a reservoir is used).

For home installations, the hood preferably houses two fans, as shown. A single steam generation unit can be used for more than one fan: as shown in FIG. 2, the reservoir 280 is connected by a conduit 282 to the pump of the steam generator, and an outlet conduit 284 joins from the steam outlet 127 through opening 129 to a manifold 288 from where the steam is directed to the fan housings and ultimately the fans. Although shown as rigid piping, flexible tubes and a simple “Y”-connection can be used to transfer the steam from the generator to the bottom portions of the fan housings. The fan blades can be metal or any plastic that will withstand the design temperature of the superheated steam exiting from the nozzle and impinging the fan blades. The plastic should not soften during the cleaning cycle (described below).

In another embodiment, a spray of water, as in the prior art, can be used in combination with the present device to treat the exhaust before it contacts the fan. Such a spray can be used to entrain smoke particles with the condensate contacting the impeller being flung into the gutter. Because of the additional water content of the exhaust stream, it is desirable to increase the flow of steam and/or its enthalpy content to account for the cooling effect of the additional water present.

An advantage of the present invention is that it uses less liquid water than the prior art devices because the water is used in the form of steam (perhaps unless an additional non-steam water spray is added). Thus, although less preferred because more water will be used, the steam generator can produce a mixed phase (liquid and vapor) at an elevated pressure sufficient to force a quantity of the mixture onto the impeller effective for degreasing, by varying the water pressure from the pump and the heat supplied.

As with prior art devices, the present device is preferably actuated through the use of a control panel 211 (including one or more buttons, switches, toggles, control knobs, etc., and optionally a simple computer or chip controller) on the hood accessible to the user, as shown in FIG. 2 (control wires to pump and heater not shown). The user actuates a cleaning cycle using the control panel, by which the controller starts a timer and actuates the heater for a set period of time (cycling on and off), for generally between 15 seconds and five minutes, with about one to two minutes being preferred. The controller can start the timer immediately or wait for a signal from the lower set point temperature regulator before the time is counted down. Shown in FIG. 2 is an input device on the control panel for the user to adjust the preset time and a display 213 indicating the duration of the cleaning cycle (e.g., a countdown until completed, and otherwise, optionally, the time of day). The electrical connections to the controller, the heating coil, the pump, and the fans are not shown in the drawings, and neither are the control lines from the temperature regulator(s) and the water level sensor.

In a more preferred embodiment, when the user actuates a cleaning cycle the generator starts to heat and once the temperature reaches the set point of the low temperature sensor (e.g., above about 130° C.) the pump is started for a fixed time, preferably about one minute. The generator will continue to heat until the temperature reaches the set point of the upper set point regulator, at which point the heating will be stopped. The pump may continue if the upper set point temperature is reached before the pump times out. Once the heating is stopped and the pump is shut off, the active portion of the cycle is ended. However, steam may continue to be generated and impinge on the blades so long as the residual heat and any water left in the generator is sufficient to generate steam.

In the prior art devices using water and detergent, actuating the device typically results in a water/detergent spray for three 15-second intervals over the period of about one minute. During that time (the 45 seconds of spraying), the prior art devices use about one liter of water. In the present invention, it is preferred that the preset time be about one to two minutes. During that time, the instant device has been tested and found to use approximately 0.1 to 0.2 liters of water. Thus, for each actuation of the cleaning device, the present invention uses about one-tenth to one-fifth the amount of water the prior art devices use, and without the presence of detergent in the water run-off.

The cooking fume load, the amount of material already adhered to the impeller, how often the steam cleaner is operated, and under what conditions it is operated are among the variables that will effect how quickly the impeller will be degreased; by “degreased” is meant removal of the grime from the impeller. For extending cooking, the controller can be provided with a timer to initiate cleaning at given intervals; for example, every 15 minutes.

The foregoing description is meant to be illustrative and not limiting. Various changes, modifications, and additions may become apparent to the skilled artisan upon a perusal of this specification, and such are meant to be within the scope and spirit of the invention as defined by the claims. 

1. A hood for ventilating a home cooking area, comprising: a hood enclosure; a fan disposed in the enclosure for exhausting cooking fumes, the fan having an impeller and a fan housing; and a steam generator within the hood enclosure for generating pressurized steam from a water supply, the steam generator having an outlet, and the outlet being fluidly connected to the fan housing effective to direct pressurized steam onto the impeller, the pressure of the steam generated being above atmospheric pressure.
 2. The hood of claim 1, further comprising a steam generator housing having a mating base and cover enclosing the steam generator, and a pump mounted on the steam generator housing and fluidly connected between the water supply and the steam generator.
 3. The hood of claim 1, wherein the steam generator further comprises a heating coil, at least one temperature regulator controlling the temperature at which the heating coil shuts off, and at least one second temperature regulator controlling the temperature at which the heating coil is turned on.
 4. The hood of claim 1, wherein the steam generator has a low profile.
 5. The hood of claim 3, further comprising a temperature-sensitive fuse controlling power to the induction heating coil by sensing the temperature of the steam generator.
 6. The hood of claim 3, wherein the steam generator comprises a base and a cover, said heating coil is disposed in the base, and a plate having a plurality of small holes and disposed immovably between the base and the cover.
 7. The hood of claim 1, further comprising a user-accessible controller for initiating a cleaning cycle, the controller including a timer, and the controller energizing the pump and the heating coil during the cleaning cycle.
 8. The hood of claim 7, further comprising a water reservoir attached to the hood and fluidly connected to the steam generator, and a low level sensor connected to the controller, the controller adapted to de-energize the heating coil on a low level sensed.
 9. A method for degreasing the impeller of a fan mounted in a cooking exhaust hood installation in a home, comprising: A. providing a hood installation including said fan; B. providing water and heating the water to steam in a low profile vessel wholly within the hood installation to generate steam above atmospheric pressure; and C. directing said steam from said vessel against the impeller of said fan in an amount effective to degrease the impeller.
 10. The method of claim 9, wherein the pressurized steam is generated at a temperature of at least about 140° C.
 11. The method of claim 10, wherein the pressurized steam is generated at a temperature of at least about 175° C.
 12. The method of claim 11, wherein the pressurized steam is generated up to a temperature of about 200° C.
 13. The method of claim 9, further comprising the step of stopping the heating when the temperature of the steam generated exceeds about 215° C.
 14. The method of claim 9, further comprising pumping water to said vessel.
 15. The method of claim 9, further comprising restricting the flow of steam from said vessel onto said impeller with a nozzle.
 16. The method of claim 9, further comprising providing a refillable reservoir of water, and providing the water by pumping the water from the reservoir, and further comprising automatically shutting off the steam generator if water in the reservoir falls below a predetermined level.
 17. The method of claim 9, further comprising cycling the heating between two predetermined temperatures for a predetermined period of time.
 18. The method of claim 17, further comprising a user-accessible control for starting the cycling.
 19. The hood of claim 1, wherein the steam generator has a low profile. 